Percentage Calculator
Three everyday percentage jobs in one place — a percentage of a value, the change between two numbers, and what percent one number is of another — each with the working shown.
Reviewed by the OmniCalc teamMethod verified 2026-07-01
36
Result 36Show steps
- Convert the percentage to a decimal: 15% = 15 ÷ 100 = 0.15.
- Multiply by the whole: 0.15 × 240 = 36.
- So 15% of 240 is 36.
How to use the percentage calculator
- 1Pick the job with the mode control: X% of Y, % change, or what % is X of Y. The input labels update to match.
- 2Type the two numbers. The answer updates as you type — there is no button to press.
- 3Open Show steps under the result to see the exact arithmetic, handy for checking homework or a spreadsheet formula.
- 4Copy the answer, or hit the star to keep the tool one tap away next time.
The three percentage formulas
X% of Y = (X ÷ 100) × Y
% change = (new − old) ÷ |old| × 100
what % = part ÷ whole × 100
Switch mode with the control above and the input labels change to match. Every result comes with a “Show steps” breakdown so you can follow — or teach — the exact arithmetic.
A percentage trap to avoid
Percentages don’t stack the way they look. A +10% rise followed by a −10% fall does not bring you back to the start: 100 → 110 → 99. Each step is taken on a different base, so apply them one at a time rather than adding or subtracting the percentages.
Worked examples
| Question | Answer |
|---|---|
| 15% of 240 | 36 |
| What is 25% of 80? | 20 |
| Change from 80 to 100 | +25% |
| Change from 100 to 75 | −25% |
| 30 is what % of 150? | 20% |
Frequently asked questions
What's the difference between percent and percentage points?
A percent is relative; a percentage point is absolute. If a rate rises from 40% to 44%, that's a 4 percentage-point rise but a 10% increase (4 ÷ 40). This calculator reports the relative percent — use the '% change' mode and read the result as a percentage.
How do I reverse a percentage — find the original before a discount?
If a price is 80 after a 20% discount, the original is 80 ÷ (1 − 0.20) = 100, not 80 + 20%. To check any reverse calculation here, use 'What % is X of Y' with the discounted and original figures and confirm you get the discount you expected.
How do I calculate a discount or a sale price?
Use 'X% of Y' to find the discount amount — e.g. 15% of 240 is 36 — then subtract it from the original (240 − 36 = 204). For a quick sale price, the amount off is the percentage of the original price.
How does percent change handle negative numbers?
Percent change is computed as (to − from) ÷ |from| × 100, dividing by the absolute value of the starting number. So a move is scaled by the size of where you started, and the sign of the result reflects the direction of the change. If the starting value is 0, percent change is undefined — division by zero — and the calculator says so instead of returning a misleading number.
Every result is computed with double-precision arithmetic and cleaned of floating-point rounding dust before display. Last reviewed 2026-07-01.